test(version): a changelog-only commit owes no changelog entry (#191)

The guard ate its own tail. A PR that adds a missing entry is itself a merged
PR with no entry, and so is the PR that adds THAT one. Three PRs into v0.9.0
before the regress was recognised as structural rather than one more edge case.

A commit that changed nothing but CHANGELOG.md has no change to describe — it
IS the description. Exempted, alongside the release cut, which is recognised as
before by touching CHANGELOG.md and version.go together.

The two rules are separate on purpose. The cut may carry other files and still
be a cut (v0.9.0's carried this very test), while changelog-only means exactly
that: one file, or the exemption does not apply. #189 changed only
version_test.go and owed an entry under both rules, which is the right answer.

Both exemptions mutation-checked: disabling either turns the test red, so
neither is defensive decoration.

Honest cost, recorded: this guard caught five genuinely missing entries in
v0.9.0 — including two user-visible fixes that would have shipped a release
page that never mentioned them — and its edges then cost three round trips.
Worth it, but not free, and the edges were all in the same place: commits whose
subject is the changelog itself.

Signed-off-by: jitokim <pigberger70@gmail.com>

Author: jitokim

cmd/oh-my-graph/version_test.go

@@ -182,22 +182,39 @@ func TestPluginManifestsMatchVersion(t *testing.T) {
 // Recognised by what it touched, not by how its subject is worded: only a
 // release cut changes CHANGELOG.md and version.go together. A wording rule
 // would be a second thing to keep in sync with a habit.
+// It also exempts a commit that changed NOTHING BUT the changelog. Such a
+// commit has no change to describe — it IS the description — and demanding an
+// entry for it makes the check eat its own tail: the PR that adds a missing
+// entry is itself missing one, and so is the PR that adds THAT. Three PRs into
+// v0.9.0 before the regress was recognised as structural rather than another
+// edge case.
 func isReleaseCut(sha string) bool {
 	out, err := exec.Command("git", "show", "--name-only", "--format=", sha).Output()
 	if err != nil {
 		return false
 	}
 	files := strings.Fields(string(out))
-	var changelog, version bool
+	if len(files) == 0 {
+		return false
+	}
+	var changelog, version, other bool
 	for _, f := range files {
 		switch f {
 		case "CHANGELOG.md":
 			changelog = true
 		case "cmd/oh-my-graph/version.go":
 			version = true
+		default:
+			other = true
 		}
 	}
-	return changelog && version
+	// A release cut writes the heading and bumps the constant together, which
+	// nothing else does — it may carry other files and still be one.
+	if changelog && version {
+		return true
+	}
+	// Changelog-only maintenance.
+	return changelog && !other
 }
 
 func TestEveryMergedPRIsInTheChangelog(t *testing.T) {